The present invention relates to a magnetic recording and readback system for use within a disk drive and, more particularly, to such a system that includes readback compensation circuitry to minimize variations in read/write and disk relationships.
In disk drives, usually utilized for storing information in conjunction with a computer, a storage device or "disk" is rotated at high speeds and a read/write head is passed across the surface of the disk without actually touching the surface. Due to the high disk rotation speeds, for example greater than 2,500 RPM, and the relatively small sizes of the disks, for example 51/4 D, the tolerances of the equipment must be very rigidly controlled. However, variations can exist between individual disks and individual read/write heads, so some variation in data recording and reading quality can exist because of variations in the disk and read/write head relationships. In the past, there have been no methods or systems to compensate for these variations, i.e. to "adapt" to the variations. Two instances where these variations become important are in adjusting the write current level and in adjusting the data pulse widths.
In a disk drive, the read/write head is supported in a manner to move very close to the surface of the spinning disk. Air currents generated by the spinning disk cause the read/write head to float or "fly" above the surface. The height the read/write head flies above the surface of the disk is critical, i.e. the amount of current used to record or write data onto the disk is very critical so the height of the read/write head above the surface affects the amount of current optimally utilized. A particular read/write head flies above the surface of a particular disk at different heights depending upon the location above the surface. Generally, the read/write head flies higher above the surface adjacent the outer radius of the disk and flies lower above the surface adjacent the inner radius of the disk. Therefore, a higher write current is utilized for the outer positions than at the inner positions of the disk.
In the past, the adjustments to the write current levels for particular read/write head and disk combinations were averaged and then a final, single set of write current levels were included within the disk drives circuitry. Problems with data interpretation have occurred because the adjustments to the write current levels were at best a compromise. Further, if a head-disk assembly (HDA) was ever changed, the correct write current level for the new HDA could be significantly different than that which was "hardwired" into the disk drives logic circuitry, thereby, increasing the disk data errors.
The other instance of where the variations become important is in adjusting the data pulse peaks. On a disk, the data is stored in the form of magnetic flux changes of one of two directions. When the read/write head passes over the disk, the transducer coil in the head is detecting magnetic direction shifts to generate an analog signal. If in a certain time window or cell a magnetic flux change has occurred then a signal or "pulse" is generated, again in analog form. The peaks of the pulses are detected and converted to digital form that corresponds to bytes of data for use within a programmable digital computer. Because of the relatively small size of the disks (51/4" D), the small size of the magnetic flux cells and the very high rotational speed of the disk, the detection of the pulse peaks is critical. On a disk, the data pulse peaks at an inner radius position are harder to detect because the pulse peaks are closer together and the pulses are wider than at the outer radius position, thus data errors can occur.
To compensate for the data pulse peak crowding or "shifting" a form of pulse peak amplitude filtering has been employed to reduce the width of the pulses so the data pulse peaks can be more easily detected. The amplitude filtering has been in the form of cosine equilization, which is hereby defined as the collection of circuit components whose purpose it is to achieve pulse width reduction by adding and subtracting even harmonics of the signal with itself. The transfer function, F(W), of this equalizer is expressed as F(W)=1-K cos (W.tau.) which defines the ratio of output to input characteristics in terms of frequency components of angular frequency, W. The terms K and .tau. refer to the slimming constant and delay, respectively. The delay, .tau., is usually fixed and the value of the slimming constant, K, is varied to achieve the correct amount of slimming for a head/disk combination.
In the past, the optimum amount of pulse width reduction or "slimming" for various locations on a disk have been averaged and the best compromise values have been stored or "hardwired" into the disk drive's circuitry. Again, as described above, if an HDA is changed, the optimum slimming values cannot be changed so even more data errors can become likely.
There exists a need for a method and related system whereby the correct write current levels and/or the correct slimming values for a particular read/write head and disk combination can be inputted into the disk drive's circuitry to "adapt" the disk drive's circuitry to the particular HDA.